This invention relates to martensitic steel alloys and in particular to such a steel, and an article made therefrom, having a unique combination of hardness and corrosion resistance, and which can be readily hardened from a wide range of solution treating temperatures.
Hitherto, AISI Type 440C alloy has been used in applications, such as bearings and bearing races, where both high hardness and corrosion resistance are required. Type 440C alloy has good corrosion resistance and provides the highest strength and hardness of the known martensitic stainless steels. Although Type 440C alloy is capable of providing a hardness of 60HRC in the as-tempered condition, the alloy provides a case hardness of only about 57-58HRC when it is hardened by induction heating. This limitation on the induction-hardened hardness of Type 440C alloy leaves much to be desired for applications that require a hardness of at least 60HRC.
The high-carbon, high-chromium tool steels, such as AISI Type D2 alloy, contain about 1-2% C and about 12% Cr. These steels provide very high hardness, for example, 60-64HRC, when properly heat treated. However, because of their lower chromium compared to stainless steels such as Type 440C, the high-carbon, high-chromium tool steels are less than desirable for applications that require good corrosion resistance.
In designing a corrosion resistant steel that provides very high hardness, i.e., hardness exceeding 60 HRC, an additional consideration is the heat treating capability of the user of such a steel. In order to facilitate the wide variety of heat treating processes that are used, it is very desirable that a high hardness, corrosion resistant steel be hardenable to its peak hardness over as wide a range of solution treating temperatures as possible.